EAELT DEVELOPMENT OF JDLUS TEREESTRIS. 221 



Borax carmine stained well in the earlier stages, wtiile the ovum 

 was still in the ovary, and also in later stages, when the embryo 

 was far advanced in development; but in the intermediate stages, 

 between about the tenth day and hatching, was wholly useless ; 

 staining the yolk-spherules equally with the nuclei. Hsema- 

 toxylin was better, staining the nuclei deeply ; but it also 

 stained the smaller yolk-spherules so as to make it a difficult 

 matter in some cases to distinguish between them and the 

 nucleoli. The best fluid was alum-carmine prepared after 

 Grenacher^s method. This fluid has the advantage of staining 

 the nuclei and nucleoli with a different tinge to that of the 

 yolk-spherules, and the result was most satisfactory. The difii- 

 culties in the way of observing the course of development were 

 many and were only overcome by cutting a great number of 

 sections, only about one series in twenty being perfectly satis- 

 factory. 



The warmth of the weather had a great influence on the rate 

 of development j one clump of eggs, for instance, was hatched 

 on the twelfth day after being laid, while another was not 

 hatched till the twenty-fifth. As the shorter period seemed to 

 be the most usual, I worked out a clump of eggs which hatched 

 on the twelfth day, and preserved a number each day, using 

 the results as a standard by which to estimate the progress of 

 development in other ova. 



I propose in the present paper to begin with the ovum in 

 the ovary after it has attained a fair size and to trace its deve- 

 lopment up to the time of hatching, leaving for a future paper 

 its further development to the adult animal. 



The Ovarian Ovum. 



The ovum within the ovary is surrounded with a follicular 

 envelope derived from the cells of the ovary. It has a large 

 nucleus and a single large nucleolus, within which it is usually 

 possible to make out two or three vesicular spaces. The body 

 of the ovum stains slightly. The nucleus is large and distinct, 

 stains slightly, and .when viewed under a high power (-j-L oil 



